Metal-mediated oxidation reactions play an important role in biological processes and in abiological reactions used in organic synthesis. The function of a large proportion of these reactions is the transfer of groups containing heteroatoms such as nitrogen and oxygen to organic molecules. Many of these processes have been postulated to proceed via metal complexes that contain reactive metal-oxygen and metal-nitrogen bonds. However, understanding of the chemistry of these functionalities and the mechanisms of their reactions lags substantially behind what is known about analogous transformations that involve metal-carbon and metal-hydrogen bonds. The goal of this proposal is the development of systematic methods for the synthesis of complexes containing metal-heteroatom bonds and for the study of the scope and mechanisms of their reactions. This will improve understanding of the mechanisms of currently known metal-mediated oxidatiorx/heteroatom transfer reactions and allow the rational development of new members of this important class of reactions. The proposal outlines the following approaches to these goals: (1) development of general methods for the synthesis of metal complexes with metal-oxygen and -nitrogen single and multiple bonds that are reactive toward organic compounds; (2) isolation and full characterization of such molecules where possible, and where it is not, their characterization by indirect methods; (3) exploration of the reactions of these materials with organic compounds; and (4) elucidation of the mechanisms of these reactions to uncover general concepts useful for understanding currently known oxidation/heteroatom transfer processes and for development of new catalytic and stoichiometric synthetic reagents.